FIG. 8 is a block diagram showing the constitution of a conventionally-known video display device that can correct luminance ranges of a display device. FIG. 9 is a diagram showing the luminance distribution in a horizontal direction (a horizontal plane).
As shown in FIG. 8, the conventionally-known video display device is constituted of a video processing unit 801, a range correction unit 802, a main control unit 803, a storage unit 804, and a video display unit 805.
In the above constitution, input video signals are processed by the video processing unit 801, which then produces processed video signals and outputs them to the range correction unit 802. The storage unit 804 stores correction values for correcting the characteristics of the individual luminance ranges of the video display unit 805 in advance. The main control unit 803 reads correction values from the storage unit 804 so as to control the range correction unit 802. The range correction unit 802 corrects processed video signals so as to eliminate the individual luminance ranges of the video display unit 805; then, it outputs range-corrected video signals, which are produced after luminance ranges are corrected, to the video display unit 805. Thus, the video display unit 805 displays video images having no luminance range.
The above conventionally-known technology corrects the luminance ranges so that a bright area is forced to match a dark area in luminance, wherein after the luminance range correction, the overall luminance of the display screen may be greatly reduced since the correction is performed to achieve 100% non-luminance range.
The known method teaches that the overall area of the display screen is not subjected to a non-luminance range condition as indicated by “correction level 100%” in FIG. 9, but a single target luminance value is set for luminance range correction, then, luminance is reduced to the target luminance range only when the present luminance is higher than the preset luminance value (see Patent Document 1, for example). For example, when the target luminance value is set to a certain luminance value indicated by “correction level 10%”, it is possible to suppress a luminance reduction to 10% compared with a luminance reduction adapted to “100% range correction”.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-196087